Mapping surface currents and waves
in Monterey Bay with HF Radar

High-frequency (HF) radar technology offers unique capabilities to map coastal ocean
currents and wave heights out to distances of about 50 km from shore. These instruments
work by observing energy backscattered from surface waves. Estimates of the currents
derive from Doppler shifts of the spectral peaks, while wave heights and directions are
related to the overall shape of the backscatter spectrum. The theory behind HF radar
measurements has been described for several decades, but practical applications have
lagged behind. Recent measurements from Monterey Bay, including Coastal Ocean Dynamics
Applications Radar (CODAR) measurements collected at MBARI, have led to much broader
acceptance within the oceanographic community.

This talk will overview the simple concepts behind HF radar, including the different
designs used by existing systems such as CODAR and Ocean Surface Current Radar
(OSCR). It
will also present results from Monterey Bay, which have led to new understanding of the
circulation. Currents, particularly during the summer months, are now known to be driven
in nearly equal proportions by eddies and upwelling filaments, sea breeze winds, and tidal
fluctuations. The two-dimensional current maps available from the HF radar network make it
possible to observe and separate the effects of these multiple driving forces.

Future uses of HF radar are certain to influence coastal oceanography as
well as public safety functions such as search and rescue, wave height predictions, and
hazardous-spill tracking and containment. Some of the remaining problems with HF radar
will be outlined with an eye toward the day when these real-time uses are commonplace.